Angeles Monge

The exploration of mechanical motion in molecular crystals under external stimuli is of great interest because of its potential applications in diverse fields, such as electronics, actuation, or sensing. Understanding the underlying processes, including phase transitions and structural changes, is crucial for exploiting the dynamic nature of these crystals. Here, we present a novel organic compound, PT-BTD, consisting of five interconnected aromatic units and two peripheral alkyl chains, which forms crystals that undergo a drastic anisotropic expansion (33% in the length of one of its dimensions) upon thermal stimulation, resulting in a pronounced deformation of their crystal shape. Remarkably, the transformation occurs while maintaining the single-crystal nature, which has allowed us to follow the crystal-to-crystal transformation by single-crystal analysis of the initial and expanded polymorphs, providing valuable insights into the underlying mechanisms of this unique thermosalient behavior. At the molecular level, this transformation is associated with subtle, coordinated conformational changes, including slight rotations of the five interconnected aromatic units in its structure and increased dynamism in one of its peripheral alkyl chains as the temperature rises, leading to the displacement of the molecules. In situ polarized optical microscopy reveals that this transformation occurs as a rapidly advancing front, indicative of a martensitic phase transition. The results of this study highlight the crucial role of a soft and flexible structural configuration combined with a highly compact but loosely bound supramolecular structure in the design of thermoelastic materials.

Noble metal elements are ubiquitous in our everyday life, from medical applications to electronic devices and synthetic chemistry. Iridium is one of the least abundant elements, and despite its scarcity, it remains essential for efficient and active catalytic processes. Consequently, the development of heterogeneous catalysts with the presence of active iridium sites is of enormous interest as it leads to the improvement of their recyclability and reusability. Here, we demonstrate a strategy to incorporate iridium atoms into metal–organic frameworks (MOFs), as part of their secondary building units (SBUs), resulting in robust and reusable materials with heterogeneous photocatalytic activity.

The pyrolysis process of multi-metal metal–organic frameworks produces complex ensembles with photocatalytic activity for water pollutant degradation.

We report a semiconducting triindole-based discotic liquid crystal (TRISMe) functionalized with six p-methylthiophenyl groups at its periphery. While initially a crystalline solid at room temperature, TRISMe transitions to a columnar hexagonal mesophase upon heating and retains this supramolecular organization upon subsequent cooling, despite having only three flexible alkyl chains attached to the core's nitrogens. The incorporation of methylthio groups effectively hinders tight molecular packing, stabilizing the columnar arrangement of this disk-shaped molecule. Single crystal analysis confirmed the high tendency of this compound to organize into a columnar architecture and the role played by the methylthio groups in reinforcing such structure. The mesomorphic behavior of TRISMe provides an opportunity for processing from its molten state. Notably, our research reveals significant differences in charge transport depending on the processing method, whether solution drop-casting or melt-based. TRISMe shows hole mobility values averaging 3 × 10^-1 cm² V^-1 s^-1 when incorporated in diode-type devices from the isotropic melt and annealed at the mesophase temperature, estimated by SCLC (space-charge-limited current) measurements. However, when integrated into solution-processed organic field-effect transistors (OFETs), crystalline TRISMe exhibits a hole mobility of 3 × 10^-4 cm² V^-1 s^-1. The observed differences can be attributed to a beneficial supramolecular assembly achieved in the mesophase in spite of its lower order. These results emphasize the material's potential for applications in easy-to-process electronic devices and highlight the potential of methylthio moieties in promoting columnar mesophases.

Metal–organic frameworks (MOFs) are appealing candidate materials to design new photoelectrodes for use in solar energy conversion because of their modular nature and chemical versatility. However, to date there are few examples of MOFs that can be directly used as photoelectrodes, for which they must be able to afford charge separation upon light absorption, and promote the catalytic dissociation of water molecules, while maintaining structural integrity. Here, we have explored the use of the organic linker anthraquinone-2, 6-disulfonate (2, 6-AQDS) for the preparation of MOFs to be used as photoanodes. Thus, the reaction of 2, 6-AQDS with Bi(III) or a combination of Bi(III) and Fe(III) resulted in two new MOFs, BiPF-10 and BiFePF-15, respectively. They display similar structural features, where the metal elements are disposed in inorganic-layer building units, which are pillared by the organic linkers by coordination bonds through the sulfonic acid groups. We show that the introduction of iron in the structure plays a crucial role for the practical use of the MOFs as a robust photoelectrode in a photoelectrochemical cell, producing as much as 1.23 mmol H₂ cm⁻² with the use of BiFePF-15 as photoanode. By means of time-resolved and electrochemical impedance spectroscopic studies we have been able to unravel the charge transfer mechanism, which involves the formation of a radical intermediate species, exhibiting a longer-lived lifetime by the presence of the iron-oxo clusters in BiFePF-15 to reduce the charge transfer resistance.

Magnetic refrigeration based on the magnetocaloric effect (MCE) in metal-organic frameworks (MOF) is regarded as an attractive approach to create more sustainable cooling systems with higher efficiency than traditional ones. Here, we report a study of the MCE in a series of rare-earth-based MOFs. We have considered the selection of the rare-earth cation by investigating materials belonging to the alpha-rare-earth polymeric framework-4 (alpha-RPF-4) MOF family, synthesized with different rare-earth cations, and observed that paramagnetic moment and saturation magnetization play an important role in enhancing the magnetic entropy change Delta S-M. The effect of structural parameters has also been considered by investigating three classes of metal-organic Gd materials built up from different types of inorganic secondary building units, including clusters (as in Gd-UiO-66), one-dimensional (as in alpha-RPF-4), and layered (as in Gd-LRH) conformations. Moreover, the analysis of the hydrostatic pressure influence reveals a significant increase in the -Delta S-M and relative cooling power (RCP) with values between 4.3 and 16.3 and 121-509 J/kg. Specifically, the RCPmax found was similar to 683 J/kg for Gd-UiO-66, which is higher than the one recently observed for Gd2SiO5 (649.5 J/kg). The present study demonstrates that the engineering of metal-organic framework systems based on high Gd densities may favor enhancing of magnetocaloric responses even at low pressures, thus promoting a new design strategy for efficient cooling devices.

Noble metals (Ag, Au, Pt, Rh, Ir, Pd, Ru and Os) are ubiquitous in our everyday life, from medical applications to electronic devices and synthetic chemistry. Iridium is one of the least abundant elements, and despite its scarcity, it remains essential for efficient and active catalytic processes. Consequently, the development of heterogeneous catalysts with presence of active iridium sites is of enormous interest as it leads to the improvement of their recyclability and reusability. Here, we demonstrate a strategy to incorporate iridium atoms into metal-organic frameworks (MOFs), as part of their secondary building units (SBUs), resulting in robust and reusable materials with heterogeneous photocatalytic activity.

A novel synthetic approach is described for the targeted preparation of multivariate metal-organic frameworks (MTV-MOFs) with specific combinations of metal elements. This methodology is based on the use of molecular complexes that already comprise desired metal-atom combinations, as building units for the MTV-MOF synthesis. These units are transformed into the MOF structural constituents through a ligand/linker exchange process that involves structural modifications while preserving their originally encoded atomic combination. Thus, through the use of heterometallic ring-shaped molecules combining gallium and nickel or cobalt, we have obtained MOFs with identical combinations of the metal elements, now incorporated in the rod-shaped secondary building unit, as confirmed with a combination of X-ray and electron diffraction, electron microscopy, and X-ray absorption spectroscopy techniques.

Bismuth metal–organic frameworks (MOFs) as heterogeneous catalysts are scarce, and there is little knowledge on the influence of the MOF features on their resulting activity and behavior. Here, we present the synthesis, characterization, and catalytic activity in the one‐pot multicomponent Strecker reaction with ketones of three new MOFs prepared with the combination of indium or bismuth and 4,4′,4′′,4′′′‐methanetetrayltetrabenzoic acid. One of them, denoted BiPF‐7, is very robust and chemically stable, and demonstrates a high activity in the formation of the desired α‐aminonitriles. The interaction of the catalytic substrates with the metal centers in this MOF has been crystallographically characterized, showcasing a concerted framework adaptability process that involves structural changes in framework components that are not directly involved in the binding of the guests.

Bismuth metal–organic frameworks (MOFs) as heterogeneous catalysts are scarce, and there is little knowledge on the influence of the MOF features on their resulting activity and behavior. Here, we present the synthesis, characterization, and catalytic activity in the one‐pot multicomponent Strecker reaction with ketones of three new MOFs prepared with the combination of indium or bismuth and 4,4′,4′′,4′′′‐methanetetrayltetrabenzoic acid. One of them, denoted BiPF‐7, is very robust and chemically stable, and demonstrates a high activity in the formation of the desired α‐aminonitriles. The interaction of the catalytic substrates with the metal centers in this MOF has been crystallographically characterized, showcasing a concerted framework adaptability process that involves structural changes in framework components that are not directly involved in the binding of the guests.